Engine intake system

ABSTRACT

An engine cover covers an engine; and an intake pipe through which the air is introduced into the engine. An intake silencer is provided adjacent to the intake pipe and suppresses air pressure fluctuations of air in the intake pipe to reduce intake sound. A portion of the intake silencer is covered with the engine cover, and a remaining portion is exposed with respect to the engine cover. An advantage is that secondary noise generated by the intake silencer and a temperature increase of air suctioned into the engine are simultaneously suppressed.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority to JP 2019-136603, filed Jul. 25, 2019, the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to an engine intake system.

BACKGROUND ART

An engine cover that covers an engine for thermal insulation and sound insulation is generally provided to an engine compartment of a vehicle. In Patent document 1, it is described that the engine compartment is provided with the engine cover in a manner to divide the engine compartment into a piping space where an intake pipe for introducing air into the engine is disposed and an accommodating space where the engine is accommodated. In this Patent document 1, the intake pipe runs on a lateral side of the engine cover, extends rearward of the vehicle, runs further around to a rear side of the engine, and is connected to the engine. According to an engine compartment structure in this Patent document 1, heat transfer from the engine to the intake pipe is suppressed by the engine cover. Thus, a temperature increase of the air flowing through the intake pipe is avoided. As a result, a reduction in density of the air is suppressed, which is advantageous for prevention of degraded intake charging efficiency of the engine.

PRIOR ART DOCUMENTS Patent Documents

[Patent document 1] JP-A-2019-34636

SUMMARY Problems to be Solved

Moreover, there is a case where the intake pipe of the engine is provided with an intake silencer that suppresses noise generated by a pressure fluctuation of the intake air. However, when being influenced by pressure fluctuations, sound is also radiated from the silencer itself. Accordingly, in order to suppress secondary noise to by the intake silencer as a generation source, the intake silencer is desirably arranged in the engine cover. However, in such a case, a temperature of the intake silencer is increased by the heat from the engine, and a temperature of the air that is suctioned into the engine through the intake silencer is increased. As a result, intake charging efficiency of the engine is degraded, which leads to a reduction in engine output.

In view of the above, an aim of the present disclosure is to simultaneously suppress secondary noise generated by an intake silencer and suppress a temperature increase of air suctioned into an engine, and further enhances a silencing function of the intake silencer.

In order to solve the above-identified and other problems, the present disclosure covers a portion of an intake silencer with an engine cover and leaves exposes a remaining portion from the engine cover.

Means for Solving the Problems

An engine intake system disclosed herein includes: an engine cover that covers an engine accommodated in an engine compartment of a vehicle;

an intake pipe through which air is introduced into the engine; and

an intake silencer that is disposed adjacent to the intake pipe and suppresses air pressure fluctuations of the air in the intake pipe to reduce intake sound.

A first portion of the intake silencer is covered with the engine cover, and a remaining portion of the intake silencer is exposed with respect to the engine cover.

According to this, radiated sound from the intake silencer is blocked by the engine cover, which is advantageous for a reduction in noise. In addition, only a portion of the intake silencer is covered with the engine cover, and the remaining portion thereof is exposed. As a result, a temperature increase of the air at the time of flowing through the intake silencer (a reduction in density of the air) is suppressed. Therefore, this is advantageous for prevention of degraded intake charging efficiency of the engine and securement of engine output.

That the first portion of the intake silencer is covered with the engine cover and the remaining portion thereof is exposed means that a temperature difference occurs in the intake silencer, with one portion at the higher temperature than another portion at a lower temperature occur. A speed of sound that propagates in air differs with air temperature. Thus, a silencing effect becomes frequency dependent that differs with temperature. As described above, the temperature difference occurs in the intake silencer, and thus can expand the frequency range that experiences the desirable the silencing effect.

In one aspect, a turbocharger that is arranged on a downstream side of the intake silencer in an air flow direction in the intake pipe and boosts a pressure of the air to be introduced into the engine is provided.

A downstream portion of the intake silencer, a portion of the intake pipe from the downstream portion of the intake silencer to the turbocharger, and the turbocharger are covered with the engine cover, and an upstream portion of the intake silencer is exposed from the engine cover except for the downstream portion.

In this case, the turbocharger serves as a noise source. The pressure fluctuation of the air occurs in the portion of the intake pipe on the upstream side of the turbocharger. However, radiated sound from a portion from the turbocharger to the downstream portion of the intake silencer is blocked and absorbed by the engine cover. In addition, the downstream portion of the intake silencer that is located on the turbocharger side is covered with the engine cover, which is effective for silencing high-frequency sound, and thus is advantageous for the reduction in the high-frequency sound caused by actuation of the turbocharger. In addition, the radiated secondary noise from the intake silencer, which is associated with silencing of this high-frequency sound, is also blocked and absorbed by the engine cover.

In one aspect, the portion of the intake silencer that is covered with the engine cover is inserted in the engine cover from a through hole that is formed in the engine cover, and

the intake silencer is elastically supported by the through hole of the engine cover using a seal member.

According to this, it is possible to suppress vibration of the intake silencer by the seal member.

In one aspect, the intake silencer is an expandable intake silencer having an expansion chamber that is formed by being bulged from the intake pipe to an opposite side from a cabin.

According to this, it is possible to suppress the radiated sound from entering the cabin from the intake silencer.

In one aspect, the expandable intake silencer is a porous expandable intake silencer having a plurality of vent holes in a separation wall that separates an intake passage, through which the air flows, and the expansion chamber from each other, and

the vent holes are opened to a portion which is separated from a portion having the highest flow rate of the air in a wall surface on the intake passage side of the separation wall and in each of which said flow rate is relatively low.

In the case where an opening is provided in the wall surface, at the time when the air flows along the wall surface, turbulence (a swirl) is generated to the air flow due to separation of the flow, and an amount of pressure loss is increased. Such a circumstance becomes more significant as the flow rate of the air is increased. Meanwhile, in the aspect, the vent holes of the separation wall are opened to the portion where the flow rate of the air is low. Thus, the turbulence of the air does not become significant. As a result, the generation of the noise by the generation of the swirl of the air and the pressure fluctuation is suppressed, and the pressure loss in the intake silencer is not significant, which is advantageous in a point of securing the intake charging efficiency of the engine.

Advantages

According to the present disclosure, the intake silencer, which suppresses air pressure fluctuation in the intake pipe to reduce the intake sound, is provided to the intake pipe, through which the air is introduced into the engine. The portion of the intake silencer is covered with the engine cover, and the remaining portion thereof is exposed (i.e., not covered by the engine cover). Therefore, it is possible to simultaneously suppress the secondary noise generated by the intake silencer and suppress the temperature increase of the air suctioned into the engine and to expand the frequency range of the intake silencer where the noise can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view illustrating an engine compartment of a vehicle.

FIG. 2 is a vertical cross-sectional view illustrating a front portion of the engine compartment.

FIG. 3 is a plan view illustrating an engine and components of intake and exhaust systems.

FIG. 4 is a perspective view illustrating the engine that is covered with an engine cover.

FIG. 5 is a perspective view in which the engine covered with the engine cover is seen from a rear side.

FIG. 6 is a perspective view illustrating a portion provided with a travel wind guiding member in the engine compartment.

FIG. 7 is a cross-sectional view that is taken along A-A in FIG. 5.

FIG. 8 is a cross-sectional view that is taken along B-B in FIG. 5.

FIG. 9 is a transverse cross-sectional view of a portion of an intake pipe that runs around to a rear side of the engine.

FIG. 10 is a perspective view in which the intake pipe is partially cut and an intake silencer is seen from behind.

FIG. 11 is a perspective view illustrating a connected portion between a rear surface cover on an intake side and a rear surface cover on an exhaust side.

MODES FOR CARRYING OUT THE DISCLOSURE

A description will hereinafter be made on a mode for carrying out the present disclosure with reference to the drawings. The following description on a preferred embodiment is essentially and merely illustrative and thus has no intention to limit the present disclosure, application subjects thereof, and application thereof.

In a front portion of a vehicle 1 illustrated in FIG. 1, right and left walls of an engine compartment 3 for accommodating an engine 2 are each constructed of a wheel apron 4, and a rear wall thereof is constructed of a dashboard 5 that defines a cabin. An apron reinforcement 6 that extends in a vehicle longitudinal direction is provided on an upper edge of each of the right and left wheel aprons 4. Front ends of the right and left apron reinforcements 6 are coupled to each other by a cross reinforcement 7 that extends in a vehicle width direction. As illustrated in FIG. 2, an upper surface of the engine compartment 3 is covered with a hood 8, and a lower surface of the engine compartment 3 is covered with an under cover 9. A front side of the engine compartment 3 is opened so as to introduce travel wind thereinto. In FIG. 1, an engine cover 10 covers the engine 2.

<Front Structure of Engine Compartment 3>

As illustrated in FIG. 1, upper and lower bumper reinforcements 11, 12, each of which extends in the vehicle width direction, are provided in a front end portion of a vehicle body. A bumper face (not illustrated) is supported by these bumper reinforcements 11, 12. A frame member 13 that extends in the vehicle width direction is provided above the upper bumper reinforcement 11. Both ends of the frame member 13 are fixed to the cross reinforcement 7.

In a back portion of the upper bumper reinforcement 11, an air introducing portion 14 is provided to introduce the travel wind into the engine compartment 3 from a portion between the lower bumper reinforcement 12 and the frame member 13. The air introducing portion 14 includes an upper wall 14 a, a lower wall 14 b, and right and left walls 14 c, and is formed to have a rectangular cross-sectional shape. The upper wall 14 a is fixed to the frame member 13, and the lower wall 14 b is fixed to the lower bumper reinforcement 12. In addition, the upper wall 14 a and the upper bumper reinforcement 11 are coupled by an oblique bar 15.

As illustrated in FIG. 2, a grille shutter 21 that regulates an introduction amount of the travel wind is fixed behind the air introducing portion 14. A radiator 22 for cooling a coolant of the engine 2 is provided at the rear of the grille shutter 21. An air inlet portion of an intake duct 25 is connected to the upper wall 14 a of the air introducing portion 14 so as to introduce air into the engine 2 from the air introducing portion 14.

<Intake and Exhaust Systems of Engine>

As illustrated in FIG. 3, the engine 2 in this embodiment is a vertically-arranged engine, a cylinder bank direction (a crankshaft longitudinal direction) of which extends in the vehicle longitudinal direction. Moreover, the vertically arranged engine includes a bank of cylinders arranged in-line and that are oriented to move vertically up and down, overtop of the crankshaft. An intake manifold is provided on one side (a vehicle left side) of the engine 2 in the vehicle width direction, and an exhaust manifold is provided on an opposite side (a vehicle right side) thereof. Hereinafter, the side where the intake manifold of the engine 2 is provided will be referred to as an intake side, and the side where the exhaust manifold is provided will be referred to as an exhaust side.

The intake duct 25 is connected to an air cleaner 26 that is arranged on the intake side of the engine. At a position near the engine 2 (on the intake side), an intake pipe 27 extends rearward of the vehicle from the air cleaner 26. The intake pipe 27 runs around behind a rear side of the engine 2 (on an upper side of a transmission 30), extends from the rear side of the engine 2 to the exhaust side of the engine 2, and is connected to a turbocharger 28. An intake silencer 29 for reducing intake noise is provided on a portion of the intake pipe 27 that extends behind the engine rear side.

A turbocharger pipe 31 extends from a compressor of the turbocharger 28 to the intake side over an upper side of the engine 2. The air, a density of which is increased by actuation of the turbocharger 28, is delivered to the intake manifold through the turbocharger pipe 31. Exhaust gas that is exhausted from a turbine side of the turbocharger 28 flows through an exhaust gas purifier 32 and is delivered rearward of the vehicle through an exhaust pipe 33. The exhaust gas purifier 33 is arranged on the exhaust side of the engine 2.

<Engine Cover>

As illustrated in FIG. 4, the engine cover 10 includes: an upper surface cover 35 that covers an upper surface of the engine 2; a lateral surface cover 36 on the intake side that covers the intake side of the engine 2 and extends in the vehicle longitudinal direction; and a lateral surface cover 37 on the exhaust side that covers the exhaust side of the engine 2 and extends in the vehicle longitudinal direction. A front side of the engine 2 is not covered with the engine cover 10 and is opened to the front.

The upper surface cover 35 is configured to include a fixed cover 35 a and a front openable cover 35 b. As illustrated in FIG. 1, a rear edge of the fixed cover 35 a is fixed to a cowl panel 39 (see FIG. 6) of the vehicle 1. A rear edge of the front openable cover 35 b is pivotally supported by a front edge of the fixed cover 35 a. The front openable cover 35 b has a front edge that is clipped to the cross reinforcement 7, and can rotate upward (can be opened) when being unclipped.

As illustrated in FIG. 5, the engine cover 10 further includes a rear surface cover 38 that covers a rear surface side of the engine 2. The rear surface cover 38 is configured to include a rear surface cover 38 a on the intake side and a rear surface cover 38 b on the exhaust side. In the rear surface cover 38 a on the intake side and the rear surface cover 38 b on the exhaust side, edges on a central side thereof overlap each other substantially at a center in the vehicle width direction of the engine 2, and overlapping portions are fixed by a clip or the like.

<Cooling of Air Flowing Through Intake Pipe with Travel Wind, or the Like>

The lateral surface cover 36 (FIG. 4 and FIG. 6) on the intake side and the rear surface cover 38 a on the intake side of the engine cover 10 serve as separation walls that are disposed between the engine 2 and the intake pipe 27 in a manner to separate both of them from each other. The air cleaner 26 is also separated from the engine 2 by the lateral surface cover 36 on the intake side. A rear end of the lateral surface cover 36 on the intake side is connected to the rear surface cover 38 a on the intake side.

As illustrated in FIG. 6, a travel wind guide 41 is provided on an outer side of a corner portion of the engine cover 10 from a rear portion of the lateral surface cover 36 on the intake side to the rear surface cover 38 a on the intake side.

The travel wind guide 41 includes a vertical wall portion 41 a that opposes the rear portion of the lateral surface cover 36 with the intake pipe 27 being interposed therebetween. As illustrated in FIG. 5, the vertical wall portion 41 a runs around to the rear side of the engine 2, that is, behind the rear surface cover 38 a from a lateral side of the lateral surface cover 36 along the intake pipe 27. Accordingly, also on the rear side of the engine 2, the vertical wall portion 41 a opposes a portion of the rear surface cover 38 a near the intake side with the intake pipe 27 being interposed therebetween. The travel wind guide 41 includes an eaves portion 41 b, which bulges to an upper side of the intake pipe 27, at an upper end of the vertical wall portion 41 a, and a lower portion of the vertical wall portion 41 a is fixed to the lateral surface cover 36 and the rear surface cover 38 a.

Furthermore, the travel wind guide 41 includes an inclined portion 41 c, which extends obliquely outward in a manner to be separated from the intake pipe 27 to the front of the vehicle, in a front end portion of the vertical wall portion 41 a located on the lateral side of the lateral surface cover 36. A front end of the inclined portion 41 c extends to the wheel apron 4 and the apron reinforcement 6 that constitute a lateral wall of the engine compartment 3. That is, the inclined portion 41 c obliquely crosses a portion between the vertical wall portion 41 a and the lateral wall of the engine compartment 3.

Moreover, as illustrated in FIG. 5, on a lower side of the travel wind guide 41, a second guide 42 that extends rearward of the vehicle and guides the travel wind from the engine 2 to the transmission 30 is provided. This second guide 42 has a U-shaped cross-sectional shape, and, at a position below the travel wind guide 41, upper and lower flanges are fixed to the separation walls, that is, a portion from the lateral surface cover 36 to the rear surface cover 38 a. The travel wind guide 41, the lateral surface cover 36, and the rear surface cover 38 a form a travel wind introducing passage 43 through which the travel wind is guided to the transmission 30.

Thus, according to the above structure, heat of the engine 2 is blocked by the lateral surface cover 36 and the rear surface cover 38 a, and is suppressed from being transferred to the intake pipe 27. In addition, the travel wind that is introduced into the engine compartment 3 and flows rearward of the vehicle on the intake side of the engine 2 is guided by the vertical wall portion 41 a of the travel wind guide 41, and flows along the intake pipe 27 from the rear portion on the intake side of the engine 2 to the rear side of the engine 2. In this way, the air that flows through the intake pipe 27 is reliably cooled by the travel wind, which is advantageous for improvement in intake charging efficiency of the engine.

In the above embodiment, the travel wind that flows rearward of the vehicle on the intake side of the engine 2 is guided in a manner to be concentrated toward the intake pipe 27 by the inclined portion 41 c provided at the front end of the vertical wall portion 41 a. Thus, an amount of the travel wind that flows along the intake pipe 27 is increased. Furthermore, the eaves portion 41 b, which bulges to the upper side of the intake pipe 27, is provided at the upper end of the vertical wall portion 41 a, and the lower portion of the vertical wall portion 41 a is fixed to the lateral surface cover 36 and the rear surface cover 38 a. Thus, the travel wind is suppressed from escaping to the portions above and below the intake pipe 27.

Just as described, the vehicle travel wind is efficiently used to cool the air flowing through the intake pipe 27, which is advantageous for the improvement in the intake charging efficiency of the engine.

In addition, since the travel wind introducing passage 43 that guides the travel wind to the transmission 30 is formed below the travel wind guide 41, the transmission 30 can efficiently be cooled by the travel wind.

<Intake Silencer>

As illustrated in FIG. 3, the intake silencer 29 that is provided in a portion of the intake pipe 27 running on the rear side of the engine 2 is a reactive-type silencer that suppresses pressure fluctuation of the air in the intake pipe 27 to reduce intake sound and, more specifically, an expandable silencer. An expanding portion 45 that forms an expansion chamber of the intake silencer 29 is bulged from the intake pipe 27 to the engine 2 side that is an opposite side from the cabin. That is, as illustrated in FIG. 7 and FIG. 8, an expansion chamber 46 (46 b, 46 c) of the intake silencer 29 is formed to be bulged from the intake pipe 27 to the opposite side (the engine 2 side) from the cabin. In this embodiment, the expansion chamber 46 is projected obliquely upward from an upper half circumferential portion on the engine 2 side of the intake pipe 27.

In addition, of the expandable silencers, the intake silencer 29 in this embodiment is a porous expandable silencer in which a plurality of vent holes 48 is formed in a separation wall 47 that separates an intake passage 27 a, through which the air to be introduced into the engine 2 flows, and the expansion chamber 46 from each other. As illustrated in FIG. 9, the expanding portion 45 is partitioned into three expansion chambers 46 a, 46 b, 46 c by partition walls. The expansion chambers 46 a, 46 b, 46 c are aligned in a longitudinal direction of the intake pipe 27. As illustrated in FIGS. 8 and 10, each of the expansion chambers 46 a, 46 b, 46 c communicates with the intake passage 27 a by the plurality of the vertically-aligned vent holes 48. Hereinafter, the expansion chambers 46 a, 46 b, 46 c will collectively be referred to as the “expansion chamber 46”.

As illustrated in FIG. 9, on the rear side of the engine 2, the intake pipe 27 is curved to be projected to the cabin side and, as illustrated in FIG. 7, a portion thereof in which the intake silencer 29 exists is curved such that a height of the intake passage 27 a is lower than both sides thereof. The air attempts to flow in the shortest distance when flowing through the intake passage 27 a from one side to another side. Thus, as a result of the curvature of the intake pipe 27 as described above, a flow rate of the air that flows along a wall surface on the intake passage 27 a side of the separation wall 47 also becomes the highest in a substantially central portion H in a vertical direction of the separation wall 47.

Thus, as illustrated in FIGS. 7, 8, 10, in this embodiment, the vent holes 48 are opened to portions that are separated to both of upper and lower sides from the portion H, in which the flow rate of the air is the highest, in the wall surface of the separation wall 47 and in each of which the flow rate is relatively low.

As illustrated in FIG. 5, the intake pipe 27 that runs out of the travel wind guide 41 and runs around to the rear side of the engine 2 extends to the exhaust side of the engine 2 in a state where an outer surface of the rear surface cover 38 a on the intake side is exposed from the rear surface cover 38 a. Then, the intake pipe 27 enters an inner side of the rear surface cover 38 b on the exhaust side from an end on an engine central side of the rear surface cover 38 b. The intake silencer 29 is arranged at a position from the rear surface cover 38 a on the intake side to the rear surface cover 38 b on the exhaust side. Accordingly, an upstream portion of the intake silencer 29 in an air flow direction of the intake pipe 27 is exposed to the outer side of the rear surface cover 38 a on the intake side, and a downstream portion thereof is covered with the rear surface cover 38 b on the exhaust side.

In summary, as illustrated in FIG. 11, in a boundary portion between the rear surface cover 38 a on the intake side and the rear surface cover 38 b on the exhaust side, the engine cover 10 is formed with a through hole 49 by denting the outer surface of the rear surface cover 38 a on the intake side to the inner side in a manner to conform to an outer shape of the intake silencer 29 and bulging an outer surface of the rear surface cover 38 b on the exhaust side to the outer side. The intake silencer 29 is inserted in the through hole 49 of the engine cover 10 and is fitted to this through hole 49 via a seal member 51. The seal member 51 is formed of a sponge material having compressibility, and the intake silencer 29 is elastically supported by the engine cover 10 using the seal member 51.

A portion of the intake pipe 27 from the downstream portion of the intake silencer 29 to the turbocharger 28 and the turbocharger 28 are covered with the rear surface cover 38 b on the exhaust side and the lateral surface cover 37 on the exhaust side from the outer side.

Thus, in the above structure, only the downstream portion of the intake silencer 29 is covered with the engine cover 10, and the upstream portion thereof is exposed to the outside and cooled by the travel wind. As a result, a temperature increase of the air at the time of flowing through the intake silencer (a reduction in the density of the air) is suppressed. Therefore, this is advantageous for prevention of the degraded intake charging efficiency of the engine 2 and securement of engine output.

In the above structure, in conjunction with the actuation of the turbocharger 28, the air pressure fluctuates in the portion of the intake pipe 27 on the upstream side of the turbocharger 28, and generates the intake sound. However, since a portion from the turbocharger 28 to the intake pipe 27 on the upstream side and the downstream portion of the intake silencer 29 is covered with the engine cover 10, radiated sound from such a portion is blocked and absorbed by the engine cover 10.

In the intake silencer 29, due to the communication between the portion thereof on the intake passage 27 a side and the expansion chamber 46 by the vent holes 48, the pressure fluctuation on the intake passage 27 a side is absorbed by the expansion chamber 46, and the intake noise is suppressed. Meanwhile, when being influenced by the pressure fluctuation, the sound is radiated from the intake silencer 29 itself. However, since the expansion chamber 46 of the intake silencer 29 is arranged on the engine 2 side as the opposite side from the cabin, an amount of the radiated noise to the cabin side is reduced. In addition, since the downstream portion of the intake silencer 29 is covered with the rear surface cover 38 b on the exhaust side, the radiated sound from the intake silencer 29 is blocked and absorbed by the rear surface cover 38 b. Therefore, transmission of secondary noise to the cabin side by the intake silencer 29 as a generation source is suppressed.

Here, that the downstream portion of the intake silencer 29 is covered with the engine cover 10 and the upstream portion thereof is exposed to the outer side and cooled by the travel wind means that a temperature difference occurs in the intake silencer 29. That is, the temperature of the downstream portion of the intake silencer 29 is higher than the upstream portion thereof. A speed of the sound that is propagated in the air differs by the temperature of the air. Thus, a frequency range with a silencing effect differs by the temperature. As described above, the temperature is generated in said intake silencer 29, and thus can exert an effect of expanding the silencing frequency range.

In the case of this example, during actuation of the engine 2, of the three expansion chambers 46 a, 46 b, 46 c that are aligned in the longitudinal direction of the intake pipe 27, the expansion chamber 46 a on the upstream side that is exposed from the engine cover 10 has the low temperature, the expansion chamber 46 c on the downstream side that is covered with the engine cover 10 has the high temperature, and the intermediate expansion chamber 46 b has the intermediate temperature. Due to the difference in the temperature among these expansion chambers 46 a, 46 b, 46 c, the silencing frequency range is expanded.

A frequency of the intake sound by the turbocharger 28 as the generation source is relatively high (several kHz). However, since the intake silencer 29 is partially covered with the engine cover 10, compared to a case where such a cover is not provided, the silencing frequency range is expanded to a high frequency side, which is advantageous for the reduction in the intake sound that is associated with the actuation of the turbocharger 28. In particular, since the portion on the turbocharger 28 side of the intake silencer 29 (the expansion chamber 46 c on the downstream side) is covered with the engine cover 10, it is possible to effectively suppress the intake sound associated with the actuation of the turbocharger 28.

In the intake silencer 29, the vent holes 48 of the separation wall 47 are opened to the portions that are separated from the portion having the highest flow rate of the air in the wall surface on the intake passage 27 a side and in each of which the flow rate is relatively low. Thus, separation of the air flow is slight in an opened portion of each of the vent holes 48 when the air flows along the wall surface of the separation wall 47. That is, disruption of the air flow does not become significant. As a result, the generation of the noise by the generation of a swirl of the air and the pressure fluctuation is suppressed, and pressure loss in the intake silencer 29 is not significant, which is advantageous in a point of securing the intake charging efficiency of the engine 2.

Furthermore, in the above structure, the intake silencer 29 is elastically supported by the engine cover 10 using the seal member 51. Therefore, vibration of the intake silencer 29 is suppressed by the seal member 51, which is advantageous for the reduction in the vibration and the sound.

DESCRIPTION OF REFERENCE SIGNS AND NUMERALS

-   -   1: Vehicle     -   2: Engine     -   3: Engine compartment     -   4: Wheel apron     -   5: Dashboard     -   6: Apron reinforcement     -   8: Hood     -   9: Under cover     -   10: Engine cover     -   27: Intake pipe     -   28: Turbocharger     -   29: Intake silencer     -   38 a, 38 b: Rear surface cover (engine cover)     -   46: Expansion chamber     -   47: Separation wall     -   48: Vent hole     -   51: Seal member 

The invention claimed is:
 1. An engine intake system comprising: an engine cover that covers an engine accommodated in an engine compartment of a vehicle; an intake pipe through which air is introduced into the engine; and an intake silencer that is disposed adjacent to the intake pipe and suppresses air pressure fluctuations of the air in the intake pipe to reduce intake sound, wherein a first portion of the intake silencer is covered by the engine cover, and a remaining portion of the intake silencer is exposed with respect to the engine cover, and the intake silencer is an expandable intake silencer having at least one expansion chamber, a portion of the expansion chamber is exposed from the engine cover and a remaining portion of the expansion chamber is covered with the engine cover.
 2. An engine intake system comprising: an engine cover that covers an engine accommodated in an engine compartment of a vehicle; an intake pipe through which air is introduced into the engine; an intake silencer that is disposed adjacent to the intake pipe and suppresses air pressure fluctuations of the air in the intake pipe to reduce intake sound, and a turbocharger that is arranged on a downstream side of the intake silencer in an air flow direction of the air in the intake pipe and boosts an air pressure of air introduced into the engine, wherein a first portion of the intake silencer is covered by the engine cover, and a remaining portion of the intake silencer is exposed with respect to the engine cover, and a downstream portion of the intake silencer, a portion of the intake pipe from the downstream portion of the intake silencer to the turbocharger, and the turbocharger are covered by the engine cover, and an upstream portion of the intake silencer is exposed with respect to the engine cover.
 3. The engine intake system according to claim 2, wherein the downstream portion of the intake silencer being the first portion of the intake silencer, and the upstream portion of the intake silence being the remaining portion of the intake silencer.
 4. An engine intake system comprising: an engine cover that covers an engine accommodated in an engine compartment of a vehicle; an intake pipe through which air is introduced into the engine; and an intake silencer that is disposed adjacent to the intake pipe and suppresses air pressure fluctuations of the air in the intake pipe to reduce intake sound, wherein a first portion of the intake silencer is covered by the engine cover, and a remaining portion of the intake silencer is exposed with respect to the engine cover, the first portion of the intake silencer that is covered with the engine cover is inserted through a through hole in in the engine cover, and the intake silencer is elastically supported by the through hole of the engine cover with a seal.
 5. The engine intake system according to claim 2, wherein the first portion of the intake silencer that is covered with the engine cover is inserted through a through hole in in the engine cover, and the intake silencer is elastically supported by the through hole of the engine cover with a seal member.
 6. The engine intake system according to claim 3, wherein the first portion of the intake silencer that is covered with the engine cover is inserted through a through hole in in the engine cover, and the intake silencer is elastically supported by the through hole of the engine cover with a seal member.
 7. The engine intake system according to claim 1, wherein the at least one expansion chamber has a bulged portion that bulges from the intake pipe away from a cabin of the vehicle.
 8. The engine intake system according to claim 2, wherein the intake silencer is an expandable intake silencer having at least one expansion chamber.
 9. The engine intake system according to claim 8, wherein the at least one expansion chamber has a bulged portion that bulges from the intake pipe away from a cabin of the vehicle.
 10. The engine intake system according to claim 3, wherein the intake silencer is an expandable intake silencer having at least one expansion chamber.
 11. The engine intake system according to claim 10, wherein the at least one expansion chamber has a bulged portion that bulges from the intake pipe away from a cabin of the vehicle.
 12. The engine intake system according to claim 1, wherein the expandable intake silencer is a porous expandable intake silencer having a plurality of vent holes in a separation wall that separates the expansion chamber and an intake passage, through which the air flows.
 13. The engine intake system according to claim 12, wherein the vent holes open to a portion of the expandable intake silencer along a wall surface on the intake passage side of the separation wall where an air flow rate is relatively low with respect to another area of the intake passage that has a higher air flow rate.
 14. The engine intake system according to claim 8, wherein the expandable intake silencer is a porous expandable intake silencer having a plurality of vent holes in a separation wall that separates the expansion chamber and an intake passage, through which the air flows.
 15. The engine intake system according to claim 14, wherein the vent holes open to a portion of the expandable intake silencer along a wall surface on the intake passage side of the separation wall where an air flow rate is relatively low with respect to another area of the intake passage that has a higher air flow rate.
 16. The engine intake system according to claim 10, wherein the expandable intake silencer is a porous expandable intake silencer having a plurality of vent holes in a separation wall that separates the expansion chamber and an intake passage, through which the air flows.
 17. The engine intake system according to claim 16, wherein the vent holes open to a portion of the expandable intake silencer along a wall surface on the intake passage side of the separation wall where an air flow rate is relatively low with respect to another area of the intake passage that has a higher air flow rate.
 18. The engine intake system according to claim 1, wherein the at least one expansion chamber comprises a first expansion chamber, a second expansion chamber, and a third expansion chamber which are aligned in a longitudinal direction of the intake pipe.
 19. The engine intake system according to claim 18, wherein the first expansion chamber on a upstream side that is exposed from the engine cover has a lower temperature than the third expansion chamber on a downstream side that is covered with the engine cover. 